Thermal protection (i.e., heat shields) for reentry vehicles, such as the Space Shuttle or the Reusable Launch Vehicle, traditionally assembled of ceramic tiles over the vehicle surface. The tiles are of relatively small area to fit the compound curves and are costly to fabricate and to bond or fasten to the surface. Upon reentry, tiles often are damaged which results in a labor-intensive, timeconsuming replacement operation. With the goal of quick turnaround for reuse of spacecraft, tiles are ineffective.
Insulating blankets made from ceramic fibers show promise, but they are used sparingly because traditional blankets made entirely from silica quickly deteriorate upon exposure to high temperatures in an oxidative environment. The blankets are initially flexible and are relatively easy to apply, but they rapidly become brittle. The lack of toughness caused by embrittlement makes the blankets susceptible to damage and forces their replacement. These silica blankets have a reuse temperature of only about 1200.degree. F. Replacing a blanket requires destroying the original blanket to remove it from the spacecraft surface, cleaning the spacecraft surface to prepare the surface for rebonding a new blanket, fabricating a replacement blanket, and positioning and adhesively bonding the replacement blanket to the surface. The delay associated with the curing of the traditional RTV silicone adhesive is up to seven days, which is unacceptable for a reusable launch vehicle where rapid turnaround is necessary for economic success.
Silica coated blankets have also been tried, but they have achieved limited success. Silica coatings are incompatible with many high temperature ceramics, including alumina, aluminosilicate, or aluminoborosilicate (e.g., Nextel), so the silica approach has only limited applicability.
Today, coated blankets must be able to withstand reentry temperatures of at least 1800-2300.degree. F. while remaining tough and flexible. The blankets should be fastenable to the surface and removable, somewhat like conventional access panels, for servicing the vehicle or for quick replacement of the insulation when it becomes damaged. Therefore, a coating solution for the blanket fibers must retain the flexibility of the fabric while deterring embrittlement upon exposure to temperatures in the 2000.degree. F. range.